Abstract: A self diagnosing apparatus and method for a fuel supply control system in an internal comustion engine are disclosed in which since an air/fuel mixture ratio feedback controlled variable is set so that an actual air/fuel mixture ratio is approached to a target (stoichiometric) air/fuel mixture ratio and movement (incremental or decremental change width) of the air/fuel mixture ratio feedback-controlled variable indicates a deviation of the actual air/fuel mixture ratio from the target air/fuel mixture ratio, a diagnosis of the air/fuel mixture ratio controlled state by means of the fuel supply control system is carried out on the basis of at least one of either a total sum of each magnitude by which the air/fuel mixture ratio feedback controlled variable is changed to enrich or enlean the air/fuel mixture ratio so as to approach it to the target air/fuel mixture ratio or a control duration of time during which the air/fuel mixture ratio feedback control variable is set to control the air/fuel mixture ratio.

Abstract: An air-fuel ratio controlling apparatus for an internal combustion engine carries out air-fuel ratio feedback control with use of oxygen sensors, which are disposed on the upstream and downstream sides of a three-way catalytic converter respectively. A correction target value for a rich/lean balance of the feedback control carried out based on the output of the upstream oxygen sensor is corrected according to the output of the downstream oxygen sensor. A control quantity for the feedback control is corrected to reduce a difference between the correction target value and an actual value. This arrangement compensates a shift of an air-fuel ratio control point due to a change in the output characteristics of the upstream oxygen sensor, prevents an excessive deviation of an air-fuel ratio, and maintains an exhaust gas at a preferable level.

Abstract: An electric air-fuel ratio control apparatus for use in an internal combustion engine provided with an oxygen sensor detecting an oxygen concentration in an exhaust gas from the engine and having such an output characteristic that the output value thereof is gradually changed with the oxygen concentration corresponding to the air-fuel ratio in a zone in the vicinity of a theoretical air-fuel ratio is disclosed. The air-fuel ratio control is performed by controlling a fuel injection quantity which is calculated mainly based on a basic fuel injection quantity and an air-fuel ratio correction coefficient in response to an output from the oxygen sensor and is performed in a manner of integration control. The control results in that it is possible to specify the air-fuel ratio in the zone in the vicinity of the aimed-value i.e. the theoretical air-fuel ratio by using the oxygen sensor according to the present invention and accordingly no response delay of the control is caused.